From a viewpoint of improving a yield in semiconductor fabrications, management of a surface condition in a periphery of a semiconductor wafer has recently been receiving attention. In semiconductor fabrication processes, a number of materials are deposited on a wafer repeatedly to form multilayer structures. As a result, unwanted materials and roughened surface are formed on the periphery which is not used for products. It has been more common in recent years to transfer the wafer by holding only the periphery of the wafer. Under such situations, the unwanted materials may come off the periphery onto device surfaces during various processes, resulting in a lowered yield. Thus, it has been customary to polish the periphery of the wafer using a polishing apparatus so as to remove the unwanted copper film and the roughened surface.
In this specification, a bevel portion, a notch portion, and an edge-cut portion will be collectively referred to as a periphery. The bevel portion is, in FIG. 1A, a portion B where a cross section has a curvature at an edge of a wafer W. A flat portion indicated by a symbol D in FIG. 1A is a region where devices are formed. A flat portion E between the device-formation region D and the bevel portion B is referred to as an edge-cut portion, which is distinguished from the device-formation region D. That is, the periphery is a rounded section extending from the edge-cut portion E to a rear surface of the wafer W. A distance from a boundary between the edge-cut portion E and the device-formation region D to the outermost periphery is approximately 6 mm. On the other hand, the notch portion is, as shown in FIG. 1B, a V-shaped cut portion formed on the edge of the wafer W, indicated by a symbol N in FIG. 1B.
A polishing apparatus using a polishing tape is known as an apparatus for removing a film formed on the bevel portion or the notch portion of the wafer (for example, see Japanese laid-open patent publications No. 8-174399 and No. 2002-93755). This type of polishing apparatus has a press pad arranged at a rear side of the polishing tape and is configured to press a polishing surface of the polishing tape against the wafer to thereby polish the bevel portion or the notch portion of the wafer.
The polishing apparatus of this type is configured to reciprocate the press pad and the polishing tape to bring the polishing surface of the polishing tape into sliding contact with the wafer to thereby polish the wafer. Typically, a mechanism for causing the reciprocation of the press pad is constituted by a cam (a rotary element) and a rod (a linearly moving element) for conversion of rotary movement into backwards-and-forwards movement. The rod is pushed against the cam by a spring and thus, contact between the cam and the rod is maintained at all times.
In order to increase a removal rate, it is typically necessary to increase a speed of the reciprocating polishing tape. However, in the above-described reciprocating mechanism, when the cam is rotated at a high speed, the linearly-moving rod cannot follow the cam and as a result, oscillation of reciprocation becomes small. There is another type of reciprocating mechanism which does not use a spring. However, this type of mechanism needs a coupling mechanism for keeping contact between the cam and the rod at all times, and a large load is exerted on the coupling mechanism. For these reasons, the conventional polishing apparatus cannot increase the removal rate greatly.